This invention relates to an installation for the filtration of a stream of contaminated fluid and more particularly to such an installation in which the filtration is accomplished by the use of a granular material capable of absorbing or adsorbing the contaminants.
Installations in accordance with the present invention, while of general application, are particularly well suited for use in the nuclear and chemical engineering industries to rid gaseous wastes of radioiodines, usually elemental iodine and methyl iodide, or of toxic gases or other contaminants. The granular material serves to trap these contaminants, either by adsorption or by absorption, and generally comprises activated carbon, zeolites or similar materials. The service life of such materials often is quite limited. To maintain good efficiency, the material must be replaced periodically, which requires the discharging and recharging of the beds provided in the filtration tanks. These operations are quite time consuming and give rise to handling and safety problems particularly in view of the hazard posed by contaminants in the material. Moreover, for maximum efficiency it is important that the material be of uniform particle size and uniformly packed. The prior charging operations often had a direct adverse effect on the uniformity of the particle size and on the packing conditions.
Heretofore, attempts to resolve these problems frequently made use of a mobile charging hopper. The hopper was supplied pneumatically and was moved into position above the beds. It was then necessary to open the tank partly at the top to permit the introduction of granular material from the hopper, thus exposing the operator and the surrounding atmosphere to contaminants from the tank.
Other known systems made use of a pneumatic conveyor arrangement in which the granular material was blown directly into the tank. These latter systems included piping disposed in the upper part of the tank, and the material was blown in bulk through openings in the lower portion of the tank. This blowing in of the material was not conducive to uniform distribution. Accordingly, to improve the distribution the material was agitated by means of vibrators, which needed to be kept in operation throughout the charging operation and which did not permit truly satisfactory packing. Moreover, the particles often struck the walls of the tank, with some of them breaking, thereby changing the particle size and producing dust that was then blown into the beds along with the particles themselves. In addition, many such prior systems required a special hopper for the bottom of the drum in which the material was shipped. The material commonly was discharged by means of a suction probe inserted into the lower part of the tank, which when withdrawn was dangerously contaminated.